Childhood-onset Obsessive Compulsive Disorder (OCD) is a chronic psychiatric disturbance that affects approximately 2-4% of children. Despite the significant risk of pervasive and compounding problems for this population, current cognitive-behavioral interventions for youth with OCD do not address the unique features of OCD in young children (ages 5-8), including: cognitive developmental differences, family context, unique symptom correlates, and a family's initial contact with the mental health system. To fill this critical gap in the knowledge base, our research group completed preliminary empirical testing for a manualized family-based cognitive-behavioral treatment (CBT) for OCD in young children. Results of the study indicate that the active treatment was associated with a moderate treatment effect. With this encouraging work as our starting point, we now propose a randomized controlled efficacy study of our family-based CBT program for young children with OCD. The proposed research aims to: (1) Compare the relative efficacy of family-based CBT to family- based Relaxation Treatment (RT) in reducing OCD symptoms in young children (aged 5-8) over 14 weeks of acute treatment, and (2) Compare the relative efficacy of family-based CBT to family based RT in reducing associated disability (functional impairment and quality of life) in young children (aged 5-8) over 14 weeks of acute treatment. Secondary aims are to: (3) Explore potential moderators and mediators of response to treatment, (4) Explore differences in time course of response, use of ASAP sessions, rates of premature termination, and drop out rates between CBT and RT over 14-weeks of acute treatment, and (5) Explore the impact of CBT and RT over a 12-month naturalistic follow-up interval on OCD symptoms, functioning, relapse rates, and utilization of other treatments. Notably, this research: (1) will evaluate outcome beyond OCD symptom reduction, including functional impairment and quality of life; (2) will examine mechanisms of change during treatment; (3) will examine time course and maintenance of response; (4) will evaluate pre- treatment patient and family characteristics that may affect treatment response and (5) represents a first step towards dissemination by evaluating the generalizability of findings across three ethnically and socioeconomically diverse sites. [unreadable] [unreadable] [unreadable]